The present invention relates generally to the control of high pressure fluid, and more particularly relates to a uniquely operative high pressure water shut-off gun which advantageously eliminates the previous necessity of dumping high pressure supply water to atmosphere during the often quite extended periods in which high pressure water is not being operatively discharged through the gun's outlet nozzle.
High pressure shut-off guns are conventionally utilized at the discharge end of a high pressure water delivery line to selectively control the operative discharge of the high pressure water to a nozzle portion of the gun which may be communicated with the high pressure water via an internal valve mechanism disposed within the gun body and actuated by a trigger lever member pivotally secured to the gun body. In the design of high pressure water shut-off guns of this general type, it has heretofore been conventional practice to provide for the dumping to atmosphere of the high pressure water through an auxiliary, relatively large opening when the gun's spray nozzle is not being used.
This dumping of the high pressure water during idle nozzle periods has been previously necessary, among other reasons, to prevent undesirably accelerated wear imposed on the internal control valve mechanism by the high pressure water.
In this context high pressure is generally pressure in excess of one thousand pounds per square inch (psi), more particularly five thousand psi and above to as high as twenty thousand psi or even higher. Anything over one thousand psi is considered quite dangerous because of the force it can exert and the velocities of fluids propelled by such high pressures. Valves which are cracked slightly open or which develop minor leakages are quickly destroyed by erosion caused by internal flow even at low flow rates.
It has additionally been thought necessary to maintain this continuous dumping of high pressure water to atmosphere during idle periods of the gun's spray nozzle to reduce the static pressure at the outlet of the system water supply pump to prevent the pump from working against a dead head created by the closed gun valve mechanism. However modern pumps and pumping systems do not prohibit deadheading.
As might be imagined, this previous necessity of continuously dumping high pressure water for lengthy periods is extremely wasteful. It would therefore be highly desirable to provide a high pressure water shut-off gun of the general type described in which the dumping of high pressure water to atmosphere was eliminated. It is accordingly an object of the present invention to provide such a high pressure water shut-off gun.
High pressure water guns must have high pressure seals which operate to seal the valve assembly from the high pressure while permitting sliding sealing contact with the valve stem. The valve stem operates the primary valve shut-off means which controls the flow between a high pressure inlet chamber and a discharge chamber leading to the nozzle of a gun, which is subject to the undesirable accelerated wear referred to previously. Because of the tight fit between the high pressure seals and the sliding operating stem of the valve mechanism, the high pressure seals tightly surround the valve stem and substantial frictional forces are thereby encountered. These frictional forces tend to cause the seals to distort or "lockup" tightly against the valve stem shaft which restricts its movement.
Although a biasing spring tends to bias the valve stem to a closed position of the valve member in the valve seat to close the pressure chamber and shut-off the flow, the biasing force supplied by the spring is at its minimum because of spring extension when the valve assembly is in the shut-off position. Frictional drag on the valve stem caused by the high pressure seals tends to prevent the primary valve member from seating fully against the valve seat thereby accentuating the erosion problem. If a stronger biasing spring is used to operate the valve stem toward the closed position, then it becomes uncomfortably difficult for the operator to hold the valve assembly open against the stronger spring. Therefore another object of the invention is to provide a pressure induced closing force which operates when the valve member is very near the seat but which does not operate when the valve member is moved slightly away from the seat, permitting the operator to hold the valve assembly open against only the biasing spring force in the open position. An improved seal having reduced resistance to movement of the valve stem with less tendency to distort or lockup on the valve stem shaft is a further object of the invention.
Because of the danger involved in the operation of high pressure guns, an additional object of the invention is to provide a safety lock to permit the operator locking the gun with the valve assembly positioned in the closed orientation and to provide a separate bleeder valve to bleed pressure from the supply line if the gun is shut-off while the pressure is still applied after the supply pump is turned off. Conventional bleeder valves tend to allow excessive bleeding during operation at high pressure, tend to clog and because of pressure induced strains, cause premature shut-off of the bleeder valve function at a pressure which is still dangerous. It is an object of the invention to provide an improved bleeder valve which does not exhibit this characteristic and bleeds consistently down to essentially zero pressure.